Engineering Yeast to Improve Heterologous Abscisic Acid Production

Abscisic acid (ABA) is a high-value product with agricultural, medical and nutritional applications. We previously constructed an ABA cell factory by expressing the ABA metabolic pathway from Botrytis cinerea in the biotechnological workhorse Saccharomyces cerevisiae. In this study, we aimed to improve ABA production and explored various rational engineering targets mostly focusing on increasing the activity of two rate-limiting cytochrome P450 monooxygenases of the ABA pathway, BcABA1 and BcABA2. We evaluated the effects of overexpression and knock-down of cell membrane transporters, expression of heterologous cytochrome b5, overexpression of a rate-limiting heme biosynthesis gene and overexpression or knock-out of genes involved in ER membrane homeostasis. One of the genes involved in ER membrane homeostasis, PAH1, was identified as the most promising engineering target. Knock-out of PAH1 improved ABA titers, but also caused a sever growth defect. By replacing the PAH1 promoter with a weak minimal promoter, it was possible to mediate the growth defect while still improving ABA production. In this report we were able to improve the ABA cell factory and furthermore provide valuable insights for future studies aiming to engineer cytochrome P450 monooxygenases. One-sentence summaryIn this study we explored various strategies to improve heterologous abscisic acid production in Saccharomyces cerevisiae and identified fine-tuning of the PAH1 gene as a promising engineering strategy.